Various cables (e.g., wireline cable and slickline cable) may be used in a wellbore to provide downhole logging tool support and communication between the downhole environment and the surface of the well. The cable may include communication cabling (e.g., fiber optics, metal conductor wires) between a wireline tool and the surface as well as the structural support to raise and lower the wireline logging tool. However, during use, friction and/or impact between the cable and the wellbore or geological formation may degrade the cable mechanical strength. Subsequently, the various structural defects may propagate along the length of the cable during downhole tool loading or service time. The weight of any logging tool may produce either static tensile stress or transient tensile stress along the slickline cable. Specifically, transient tensile stress events may lead to formation of various internal structural defects, such as cracking and delamination in a polymer composite material based cable. Such structural defects may be localized and may not show obvious influence on cable performance at initial status. However, continuous tensile stress loading may trigger a percolation threshold. The initial nano-structural or micro-structural defects may grow along the loading axis and propagate quickly, resulting in the slickline cable having non-uniform stress loading response.
Conventional nondestructive inspection methods, include laser ultrasonic, transient thermography, microwave, THz-wave, RF, eddy current, or x-ray radiography, used for small-scale structural defects evaluation as a point-inspection technique. Some of these techniques are used during manufacture of slickline cables (e.g., eddy current sensor technique for conductive cable fabrication). Point inspection of slickline cable made from a polymer composite material with reinforced carbon fibers may provide a baseline quality assurance. These techniques may be impractical, however, for analyzing a slickline or wireline cable for inspecting the full length of the cable in an oil field environment.
In addition, manufacturing process-induced structural defects may be too small to be detected. The dynamic loading stress during a downhole tool logging service may facilitate the growth and propagation of different undetected structural defects (e.g., cracks, delamination, voids etc.). Because they provide point-inspection, the above inspection techniques cannot provide a reliable method to effectively scan structural defects along the full length of the cable within a reasonable time for avoiding catastrophic cable failures while in use. There are resulting needs to detect cable structural defects and any mechanical strength degradation trend.